The fire onboard an empty Boeing 787 Dreamliner at London's Heathrow airport was linked to an Emergency Locator Transmitter (ELT) system produced by Honeywell International, the UK's Air Accidents Investigation Branch (AAIB) said in a report today.

That unit, the RESCU406AN, is present on all Dreamliners, a Boeing spokesperson confirmed.

According to the AAIB, Honeywell has produced about 6,000 units of the model, "which are fitted to a wide range of aircraft."

This is the first "significant thermal event" associated with the ELT, which uses a set of Lithium-Manganese Dioxide batteries to transmit the plane's location in the event of a crash.

The AAIB has recommended the FAA order the device be made inert in 787s "until appropriate airworthiness actions can be completed," and that it and other regulatory agencies review similar ELT systems in other types of aircraft.

In a statement, Boeing said it supports both of the AAIB's recommendations as "reasonable precautionary measures," and stands by the safety and "overall integrity" of the Dreamliner.

As Leeham News and Comment points out, a different Honeywell ELT model, the RESCU 406S, was subject to a Canadian airworthiness directive in December 2009 for "potential failure to transmit the required 406 MHZ coded signal."

As a safety-first focused company, we support the AAIB’s proposal and will offer assistance to Boeing and the airlines if needed. The investigation continues, and it’s premature to jump to conclusions. Temporarily addressing the ELTs on Boeing 787s as a precautionary measure is prudent.

The Boeing 787 ELT product action is a straightforward process, and we do not anticipate any material financial impact to Honeywell. We also support conducting safety reviews for installations of any lithium battery-powered ELTs from the variety of manufacturers who sell them.